feat: added monitoring for postgres query result (#6736)

Co-authored-by: Dalton Pearson <dalton.pearson@praemo.com>

server/monitor-types/postgres.js

@@ -3,26 +3,61 @@ const { log, UP } = require("../../src/util");
 const dayjs = require("dayjs");
 const postgresConParse = require("pg-connection-string").parse;
 const { Client } = require("pg");
+const { ConditionVariable } = require("../monitor-conditions/variables");
+const { defaultStringOperators } = require("../monitor-conditions/operators");
+const { ConditionExpressionGroup } = require("../monitor-conditions/expression");
+const { evaluateExpressionGroup } = require("../monitor-conditions/evaluator");
 
 class PostgresMonitorType extends MonitorType {
     name = "postgres";
 
+    supportsConditions = true;
+    conditionVariables = [new ConditionVariable("result", defaultStringOperators)];
+
     /**
      * @inheritdoc
      */
     async check(monitor, heartbeat, _server) {
-        let startTime = dayjs().valueOf();
-
         let query = monitor.databaseQuery;
         // No query provided by user, use SELECT 1
         if (!query || (typeof query === "string" && query.trim() === "")) {
             query = "SELECT 1";
         }
-        await this.postgresQuery(monitor.databaseConnectionString, query);
 
-        heartbeat.msg = "";
-        heartbeat.status = UP;
-        heartbeat.ping = dayjs().valueOf() - startTime;
+        const conditions = monitor.conditions ? ConditionExpressionGroup.fromMonitor(monitor) : null;
+        const hasConditions = conditions && conditions.children && conditions.children.length > 0;
+
+        const startTime = dayjs().valueOf();
+
+        try {
+            if (hasConditions) {
+                // When conditions are enabled, expect a single value result
+                const result = await this.postgresQuerySingleValue(monitor.databaseConnectionString, query);
+                heartbeat.ping = dayjs().valueOf() - startTime;
+
+                const conditionsResult = evaluateExpressionGroup(conditions, { result: String(result) });
+
+                if (!conditionsResult) {
+                    throw new Error(`Query result did not meet the specified conditions (${result})`);
+                }
+
+                heartbeat.status = UP;
+                heartbeat.msg = "Query did meet specified conditions";
+            } else {
+                // Backwards compatible: just check connection and return row count
+                const result = await this.postgresQuery(monitor.databaseConnectionString, query);
+                heartbeat.ping = dayjs().valueOf() - startTime;
+                heartbeat.status = UP;
+                heartbeat.msg = result;
+            }
+        } catch (error) {
+            heartbeat.ping = dayjs().valueOf() - startTime;
+            // Re-throw condition errors as-is, wrap database errors
+            if (error.message.includes("did not meet the specified conditions")) {
+                throw error;
+            }
+            throw new Error(`Database connection/query failed: ${error.message}`);
+        }
     }
 
     /**
@@ -76,6 +111,75 @@ class PostgresMonitorType extends MonitorType {
             });
         });
     }
+
+    /**
+     * Run a query on Postgres
+     * @param {string} connectionString The database connection string
+     * @param {string} query The query to validate the database with
+     * @returns {Promise<(string[] | object[] | object)>} Response from
+     * server
+     */
+    async postgresQuerySingleValue(connectionString, query) {
+        return new Promise((resolve, reject) => {
+            const config = postgresConParse(connectionString);
+
+            // Fix #3868, which true/false is not parsed to boolean
+            if (typeof config.ssl === "string") {
+                config.ssl = config.ssl === "true";
+            }
+
+            if (config.password === "") {
+                // See https://github.com/brianc/node-postgres/issues/1927
+                reject(new Error("Password is undefined."));
+                return;
+            }
+            const client = new Client(config);
+
+            client.on("error", (error) => {
+                log.debug(this.name, "Error caught in the error event handler.");
+                reject(error);
+            });
+
+            client.connect((err) => {
+                if (err) {
+                    reject(err);
+                    client.end();
+                } else {
+                    // Connected here
+                    try {
+                        client.query(query, (err, res) => {
+                            if (err) {
+                                reject(err);
+                            } else {
+                                // Check if we have results
+                                if (!res.rows || res.rows.length === 0) {
+                                    reject(new Error("Query returned no results"));
+                                    return;
+                                }
+                                // Check if we have multiple rows
+                                if (res.rows.length > 1) {
+                                    reject(new Error("Multiple values were found, expected only one value"));
+                                    return;
+                                }
+                                const firstRow = res.rows[0];
+                                const columnNames = Object.keys(firstRow);
+                                // Check if we have multiple columns
+                                if (columnNames.length > 1) {
+                                    reject(new Error("Multiple columns were found, expected only one value"));
+                                    return;
+                                }
+                                resolve(firstRow[columnNames[0]]);
+                            }
+                            client.end();
+                        });
+                    } catch (e) {
+                        reject(e);
+                        client.end();
+                    }
+                }
+            });
+        });
+    }
 }
 
 module.exports = {